G4S is poised to take a bigger hit over the Olympics security fiasco than the £50m it had estimated, according to reports.

The FTSE 100 company, which is in the final stages of negotiations with Games organisers Locog, is expected to incur a total loss of between £50m and £100m.

The two sides have been in talks over a final settlement for the £240m security contract, after G4S failed to provide all of its 10,400 contracted guards. The shortfall left the government with no choice but to step in with military personnel.

Two G4S directors resigned after an independent review into the company's botched London Olympics contract, which saw the group fill only 83% of its contracted shifts.

The chief operating officer, David Taylor-Smith, and Ian Horseman Sewell, head of global events, quit over the fiasco; the chief executive, Nick Buckles, stayed in post.

G4S, the world's biggest private security company with more than 650,000 staff worldwide, has also lost a Ministry of Defence contract to investigate alleged war crimes by British troops in Iraq.